JAC Board Class 9th Science Chapter 13 Notes Why Do We Fall Ill
→ Health: Health is a state of being free from illness or injury. According to the World Health Organisation (WHO), health is defined as a state of complete physical, mental and social well-being and not merely the absence of disease or infirmity.
→ Conditions essential for Good Health:
- Balanced and nutritious diet.
- Personal hygiene.
- Clean environment and surroundings.
- Healthy and pollution free air in the surroundings.
- Regular exercise.
- Proper rest.
- Good standard of living and economic status.
→ Disease: When the body is not at ease, i.e., comfortable, it is said to have a disease. In this condition, the functioning or appearance of one or more systems of the body changes. Depending on the duration, diseases are classified as acute or chronic.
a. Acute diseases: The diseases which last for a short duration of time are called acute diseases. Being of short duration, the acute diseases are unable to cause major ill effects on health, for example, common cold, malaria, typhoid, etc.
b. Chronic diseases: The diseases which last for a long duration of time or even for a lifetime are called chronic diseases. As these diseases remain in the body for a long time, their effects on the body are severe, e.g., diabetes, tuberculosis, etc.
→ Causes of a disease:
a. Immediate cause: The organisms that enter our body and cause diseases are called immediate causes, for example, virus, bacteria, protozoa, etc.
b. Contributory cause: The secondary factors which cause these organisms to enter our body are called contributory causes, e.g., dirty water, unclear surroundings, contaminated food, improper nourishment, poverty, poor standard of living, etc.
→ Diseases may be infectious or non- infectious
a. Infectious diseases: Diseases, where microbes are the immediate cause, are called infectious diseases. The infectious diseases spread from one person to another.
b. Non-infectious diseases: Some diseases that do not spread in the community but remain internal are called non-infectious diseases. Example: cancer, genetic abnormalities, high blood pressure, etc.
→ Infectious diseases: When a disease causing organism enters our body, it causes infection. It multiplies and grows in the body of the host.
| Pathogen | Diseases |
| Bacteria | Tuberculosis, tetanus, typhoid, cholera |
| Virus | AIDS, polio, chickenpox, rabies, measles |
| Fungi | Skin diseases, food poisoning |
| Protozoan | Malaria, amoebiasis, kala-azar |
| Worm | Filariasis |
→ Infectious diseases spread through:
- Air: This occurs through the little droplets thrown out by the infected person who sneezes or coughs. Someone standing closeby can breathe in these droplets and the microbes get a chance to start a new infection. Examples: common cold, pneumonia, tuberculosis.
- Water: This occurs if excreta of someone suffering from an infectious disease, such as cholera, gets mixed with the drinking water used by the people nearby. The cholera causing microbes will enter new hosts through the water they drink and cause disease in them.
- Contact: Many diseases spread by contact of the infected person with the healthy person. Examples: fungal infection, scabies, etc. AIDS and syphilis spread by sexual contact.
- Body fluids: Infected body fluids like blood, semen, mother’s milk etc., when in contact, can also cause diseases. Example-AIDS.
→ Antibiotics: Antibiotics are the drugs that kill bacteria. They commonly block the biochemical pathways important for bacteria. Many bacteria make a cell wall to protect themselves. The antibiotic penicillin blocks the bacterial processes that build the cell wall. As a result, the growing bacteria become unable to make cell walls and die easily.
→ Inflammation: When an active immune system releases many cells at the affected tissue to kill-off the disease-causing microbes, it is called inflammation. Local effects caused in the body due to inflammation are – swelling, pain, fever and redness.
→ Principles of Treatment: There are two methods for the treatment of diseases:
a. by reducing the symptoms of the diseases.
b. by killing the microbes.
→ Principles of Prevention: These are the ways to prevent the diseases.
a. General ways: The general ways of preventing infections mostly relate to preventing exposure to the diseases. We can prevent exposure to the infectious microbes as follows:
- For air-borne infections: We can prevent exposure by providing living conditions that are not over crowded.
- For water-borne infections: We can prevent exposure by using safe drinking water. This can be done by treating the water for any microbial contamination.
- For vector-borne infections:
We can prevent exposure by providing clean environment which are free from mosquitoes, flies, rats, etc.
Another general way of preventing the diseases is the availability of proper and sufficient food for everyone. This will help the immune system to become healthy and work properly for fighting off the microbes causing the disease.
b. Specific ways: By giving vaccines, i.e., childhood immunisation that is given to the children for preventing infectious diseases. During vaccination, we put dead or weakened pathogens in the body that mimics antigens we want to vaccinate against. This does not actually cause the disease but this would prevent any further exposure to the infecting microbes from turning into actual disease. Vaccinations are available for the following diseases: tetanus, diphtheria, whooping cough, measles, polio, rabies, etc.